A pump device of a rotary type for a vehicle brake control system is known in the art, for example, as disclosed in Japanese Patent Publication No. H07-217567, according to which a structure for coupling two rotary shafts is applied to the pump device. In the pump device of the rotary type, a pump shaft is rotatably supported by two bearings, while a motor shaft is rotatably supported by other two bearings. Namely, in the pump, the pump shaft and the motor shaft are respectively supported by independent bearings. According to such a structure, misalignment may be generated between the pump shaft and the motor shaft during an assembling process. Therefore, a coupling mechanism may be provided between the pump and motor shafts in order to absorb such misalignment between the shafts.
According to the structure of the above mentioned prior art, the pump shaft and the motor shaft are respectively supported by their own two bearings. Therefore, a space for arranging those four bearings in an axial direction is necessary, which may cause a problem that the pump device may become too long in the axial direction. It is, of course, necessary to provide the coupling mechanism for the purpose of absorbing the misalignment of the shafts when assembling an electric motor to a pump body of the pump device. In addition, wear-out may occur in the coupling mechanism. The coupling mechanism may become too large, if a long life should be ensured in view of the wear-out. In other words, the pump device may inevitably become too large in size.